1. Field of the Invention
The present invention relates to a phase shifting mask and a method of manufacturing the same, and more particularly, to a phase shifting mask and a method of manufacturing the same to be used in a photolithography process for forming fine patterns in a semiconductor device.
2. Discussion of the Related Art
As the integration and density of a semiconductor device increase, sizes of its unit elements decrease. This results in the decrease of the line-width of a conducting wire and other similar elements of the semiconductor device. Therefore, when forming a fine pattern, a photolithography process utilizing exposure methods, such as a contact printing method, a proximity printing method, and a projection printing method, has limitations. Accordingly, in order to form a fine pattern, the exposure methods need to be improved by using an electron beam or an ion beam, or a phase shifting mask needs to be utilized when the exposure is carried out.
Phase shifting mask generally includes a phase shifting region and a transmitting region. The phase of light that passes the phase shifting region is shifted by 180.degree., thereby causing an offset interference with light that passes the transmitting region. As a result, the resolution and the depth of the focus are improved, making it possible to obtain a good quality miniature pattern.
Phase shifting masks can be classified into alternated type, rim type, attenuated type, and outrigger type, etc. For example, a conventional alternated type phase shifting mask is disclosed in Japanese Laid-Open Patent No. 6-35169 (laid-open date: Feb. 10, 1994), entitled "A method of manufacturing a phase shifting mask".
FIGS. 1A to 1D are cross-sectional views illustrating a method of manufacturing a phase shifting mask, according to the conventional method.
Referring to FIG. 1A, an indium tin oxide (ITO) layer is deposited on a transparent substrate 11 according to a sputtering method, thereby forming a transparent conductive layer 13. A phase shifting layer 15 such as a silicon oxide layer or spin on glass (SOG) layer is formed on the transparent conductive layer 13. On the phase shifting layer 15, chrome is deposited by a sputtering method to form a light shielding layer 17. A photoresist film 18 is then coated on the light shielding layer 17.
Referring to FIG. 1B, the photoresist film 18 is exposed and developed, thereby exposing a predetermined part of the light shielding layer 17. Using the photoresist film 18 as a mask, the exposed part of the light shielding layer 17 is dry etched to expose the phase shifting layer 15. Here, the remaining light shielding layer 17 becomes a shading region.
Referring to FIG. 1C, the photoresist film 18 is removed. Then, a photoresist film 19 is coated again on the phase shifting layer 15 and the light shielding layer 17. The photoresist film 19 is exposed and developed, thereby exposing a predetermined part of the phase shifting layer 15.
Referring to FIG. 1D, using the photoresist film 19 as a mask, the exposed part of the phase shifting layer 15 is dry etched. Then, the photoresist film 19 is removed. At this time, a region where the light shielding layer 17 and the phase shifting layer 15 are removed becomes a transmitting region 14. A region where the light shielding layer 17 is removed and the phase shifting layer 15 is not removed becomes a phase shifting region 12.
However, in the conventional method of manufacturing a phase shift mask, when the phase shifting layer is etched to define the transmitting region, it is difficult to align the photoresist pattern with the transmitting region. Further, the transmitting region is defined by a photolithography method, thereby complicating the process.